code: def overlap_matrix(basis_functions):
      r"""Return a function that computes the overlap matrix for a given set of basis functions.
  
      Args:
          basis_functions (list[~qchem.basis_set.BasisFunction]): basis functions
  
      Returns:
          function: function that computes the overlap matrix
  
      **Example**
  
      >>> symbols  = ['H', 'H']
      >>> geometry = np.array([[0.0, 0.0, 0.0], [0.0, 0.0, 1.0]], requires_grad = False)
      >>> alpha = np.array([[3.42525091, 0.62391373, 0.1688554],
      >>>                   [3.42525091, 0.62391373, 0.1688554]], requires_grad=True)
      >>> mol = qml.qchem.Molecule(symbols, geometry, alpha=alpha)
      >>> args = [alpha]
      >>> overlap_matrix(mol.basis_set)(*args)
      array([[1.0, 0.7965883009074122], [0.7965883009074122, 1.0]])
      """
  
      def overlap(*args):
          r"""Construct the overlap matrix for a given set of basis functions.
  
          Args:
              *args (array[array[float]]): initial values of the differentiable parameters
  
          Returns:
              array[array[float]]: the overlap matrix
          """
          n = len(basis_functions)
          matrix = qml.math.eye(n)
  
          for (i, a), (j, b) in it.combinations(
              enumerate(basis_functions), r=2
          ):
              args_ab = []
              if args:
                  args_ab.extend([arg[i], arg[j]] for arg in args)
              integral = overlap_integral(a, b, normalize=False)(
                  *args_ab
              )
  
              o = qml.math.zeros((n, n))
              o[i, j] = o[j, i] = 1.0
              matrix = matrix + integral * o
  
          return matrix
  
      return overlap
  
file_path: pennylane/pennylane/qchem/matrices.py
imports: import itertools
  import numpy
  import pennylane
  from .integrals import attraction_integral, kinetic_integral, moment_integral, overlap_integral, repulsion_integral
label_desc: Use image node_id 2 for calling a global function with example usage: overlap_matrix(basis_functions) and returns: overlap, matrix